1. Field of the Invention
This invention relates to a signal correcting method for use in a radiation image read-out apparatus. This invention particularly relates to a signal correcting method for use in a radiation image read-out apparatus, in which light emitted by a stimulable phosphor sheet is detected with a line sensor.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a stimulable phosphor sheet, which comprises a substrate and a layer of the stimulable phosphor overlaid on the substrate. Stimulating rays, such as a laser beam, are deflected and caused to scan pixels in the radiation image, which has been stored on the stimulable phosphor sheet, one after another. The stimulating rays cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted successively from the pixels in the radiation image having been stored on the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal by photoelectric read-out means. The stimulable phosphor sheet, from which the image signal has been detected, is then exposed to erasing light, and radiation energy remaining thereon is thereby released.
The image signal, which has been obtained from the radiation image recording and reproducing systems described above, is then subjected to image processing, such as gradation processing and processing in the frequency domain, such that a visible radiation image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness, can be obtained. The image signal having been obtained from the image processing is utilized for reproducing a visible image for diagnosis, or the like, on film or on a high resolution cathode ray tube (CRT) display device. In cases where the stimulable phosphor sheet, from which the image signal has been detected, is then exposed to the erasing light, and energy remaining on the stimulable phosphor sheet is thereby released, the erased stimulable phosphor sheet is capable of being used again for the recording of a radiation image.
Novel radiation image read-out apparatuses for use in the radiation image recording and reproducing systems described above have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540. In the proposed radiation image read-out apparatuses, from the point of view of keeping the emitted light detection time short, reducing the size of the apparatus, and keeping the cost low, a line light source, such as a fluorescent lamp, a cold cathode fluorescent lamp, or a light emitting diode (LED) array, for irradiating linear stimulating rays onto a stimulable phosphor sheet is utilized as a stimulating ray source, and a line sensor comprising a plurality of photoelectric conversion devices arrayed along the length direction of a linear area of the stimulable phosphor sheet, onto which linear area the stimulating rays are irradiated by the line light source, (i.e., the width direction of the stimulable phosphor sheet) is utilized as photoelectric read-out means. Also, the proposed radiation image read-out apparatuses comprise scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet.
In the aforesaid types of radiation image read-out apparatuses, it is necessary for the length of the line sensor to be identical with or longer than the width of the stimulable phosphor sheet. However, it is not always possible to produce the line sensor, which has the length identical with or longer than the width of the stimulable phosphor sheet, with a single production process. Therefore, a line sensor, which has the length identical with or longer than the width of the stimulable phosphor sheet, has heretofore been constituted by arraying a plurality of line sensor constituting units, each of which has a length shorter than the width of the stimulable phosphor sheet, such that certain regions of adjacent line sensor constituting units overlap each other with respect to the direction normal to the length direction of each of the line sensor constituting units. Also, radiation image read-out apparatuses have heretofore been proposed, wherein a plurality of line sensors are utilized, light emitted from a linear area of a stimulable phosphor sheet is detected with each of the line sensors, and an image signal representing a radiation image is obtained from signal values obtained from each of the line sensors.
However, in the radiation image read-out apparatuses described above, the plurality of the line sensor constituting units are arrayed such that certain regions of the line sensor constituting units overlap each other. Therefore, if position matching processing with respect to the width direction of the stimulable phosphor sheet is not performed on signal components having been obtained from the line sensor constituting units, image patterns obtained from the line sensor constituting units will shift, and the image quality of the obtained radiation image will become bad. Also, in the radiation image read-out apparatuses described above, wherein the plurality of the line sensors are utilized, if the position matching processing with respect to the width direction of the stimulable phosphor sheet is not performed on signal components having been obtained from the line sensors, the image patterns obtained from the line sensors will shift, and the image quality of the obtained radiation image will become bad.